SECTION 17.9 : casting to duration types
Fourth bullet, casting from xdt:yearMonthDuration or
xdt:dayTimeDuration to xs:duration, it is not necessary to
cast SV to string before casting to duration. The source
value is already a duration; all you have to do is change the
type annotation on it, as explained in section
17.3 "Casting from derived types to parent types".
- Steve B.